A rather intriguing scenario involves the rare-earth 5\(d\)  itinerant electrons, which may interact or hybridize strongly with the magnetic Ni orbitals, leading to new physics absent in the cuprates [1]}. Measurements of the Hall coefficient show that the charge carriers change from electron-like to hole-like upon doping, suggesting the presence of an electron pocket in the parent compound of infinite-layer nickelates [2]}, and reinforcing the basic electronic structure from DFT analysis [3]}, [1]}. At the same time, both resonant inelastic x-ray scattering (RIXS) and EELS measurements have highlighted the essential contributions from the rare-earth 5\(d\)  orbitals [5]}, [6]}. Whether or not Kondo physics is relevant in these material remains unclear; however, the experimental results provide strong evidence that multi-orbital models, which include the Ni \(d_{x^2-y^2}\)  orbital representing physics within the Ni-O plane and the \(R\)  5\(d\)  orbital featuring itinerant electrons from the rare-earth elements, could be strong candidates to describe the low-energy physics of the infinite-layer nickelates.
